What should I do if I may have to move to another state after enlisting in the National Guard, but prior to attending basic training?

You always have a choice, you haven't even started Basic. Talk to your recruiter's boss. Let him know your next step if not resolved quickly is to contact your state representative of your district.

OK, the first step it to talk to your readiness NCO as soon as you confirm you are moving. He will make sure that you don't have any existing flags (weight, APFT, etc) and then will send your packet to the Interstate Transfer Coordinator at your State Headquarters, who will contact the gaining state to find you a slot in your MOS. Once they find you a home, the process is pretty simple. If the gaining state doesn't have an open slot, you may have to wait or may have to reclass to a new MOS. Artillery units are pretty common in the Guard and Texas is a huge state, so I don't think you will have an issue there. Since you are so close to shipping, PVC Herrington is probably correct that they will not do anything until you finish AIT. When you get back, be aware that you can ask to drill with a local unit until they can get you transferred.